Merge branch 'feature_make_standalone' into 'master'

Classes/Backend/Ajax.php

Classes/Controller/YoutubeController.php

Classes/EventListener/PluginRenderer.php

Classes/Form/Element/LicenceStatus.php

Classes/Hooks/LicenceCheckHook.php

Classes/Hooks/PageLayoutView/PluginRenderer.php

Classes/Preview/PreviewRenderer.php

Classes/Preview/PreviewService.php

Classes/Service/CachedImageService.php

Classes/Service/ExtensionSettingsService.php

Classes/Service/LicenceCheckService.php

Classes/Service/YoutubeService.php

Classes/ViewHelpers/RenderSvgViewHelper.php

Classes/ViewHelpers/StructuredVideoDataViewHelper.php

Classes/ViewHelpers/UrlWithQueryParametersViewHelper.php

Configuration/Backend/AjaxRoutes.php

Configuration/FlexForms/flexform_sgyoutube_youtube.xml

Configuration/Services.yaml

Configuration/TypoScript/setup.typoscript

README.md